EIGHTH LECTURE. 



OBSERVATIONS ON VARIOUS NUCLEOLAR 

 STRUCTURES OF THE CELL. 



THOS. H. MONTGOMERY, JR. 



(Lecture given Attgust j, 1898.} 



WITHIN cells occur structures of various kinds which have 

 been loosely termed " Nucleoli." In the strict sense of the 

 term, however, the word " nucleolus " should be applied solely 

 to those elements of the nucleus which, with suitable double 

 stains, such as haematoxylin-eosin, or the Ehrlich-Biondi-Hei- 

 denhain mixture, stain differently from the chromatin, at least 

 when the latter substance is in the -chromosome stage. Thus 

 the term "nucleolus," introduced by Valentin in 1839, corre- 

 sponds to the " plasmosoma " of Ogata, 1883. 



Besides the true nucleolus, as just defined, numerous other 

 so-called " nucleolar " structures occur in various cells. Among 

 them are the karyosomes, which are merely thickened nodal- 

 points of the chromatin reticulum ; further, what I shall term 

 the " chromatin-nucleus," which is found in certain spermato- 

 cytes ; and then various structures, which stain neither like the 

 true nucleolus nor the chromatin, and to which such terms 

 as " Paranucleoli," " Nebennucleoli," and " Pseudonucleoli " 

 have been applied. It is one of the most difficult questions to 

 determine the nature and correspondence of the latter struc- 

 tures, and very .extensive comparative studies are necessary for 

 their elucidation. But from the cases studied by me, it would 

 appear that some of these structures in Metazoa probably must 

 be placed within the category of true nucleoli, and be regarded 

 as true nucleoli of a different chemical nature. That is to say, 



